Organopolysiloxanes can be prepared by the polymerization of low-molecular-weight organosiloxanes and molecular chain end-blocking agent (added to regulate the degree of polymerization) under strong acid or strong base catalysis. This polymerization is followed by neutralization of the catalyst. The preparation of organopolysiloxanes under strong acid catalysis is typically run as follows.
An organosiloxane is first polymerized in the presence of a strong acid catalyst. After polymerization the organopolysiloxane is washed with water, and the strong acid catalyst is then neutralized by the addition of a solid neutralizing agent such as sodium carbonate, sodium bicarbonate. calcium carbonate, magnesium carbonate, or ammonium carbonate. The excess neutralizing agent and the neutralization salt(s) produced by the neutralization reaction(s) are filtered off, and the organopolysiloxane product is recovered by heating the filtrate in vacuo in order to remove low-boiling components such as unreacted organosiloxane.
However, because this neutralization reaction is run in a heterogeneous system, the neutralization times are exceedingly long. Moreover, because a nearly complete neutralization of the strong acid catalyst cannot be achieved, another problem here is that the organopolysiloxane yield is reduced by a depolymerization which occurs when the organopolysiloxane is heated in vacuo after neutralization. An additional problem with organopolysiloxane produced by this method is that it has an impaired heat resistance due to the presence of residual unneutralized strong acid catalyst.
In another vein, the heat resistance of organopolysiloxanes obtained from such polymerization is also impaired by the presence of terminal silanol groups rather than the molecular chain end-blocking group added for the purpose of regulating the degree of polymerization.
In order to solve the problems described above. investigations were conducted into various organopolysiloxane preparative methods, for example, (a) organosiloxane polymerization under strong acid catalysis followed by the addition of aqueous ammonia to the system, and (b) organosiloxane polymerization under strong acid catalysis followed by addition to the system of water and the organosilicon compound (R.sup.1.sub.3 Si).sub.2 NH or R.sup.1.sub.3 SiNHR.sup.2 wherein R.sup.1 and R.sup.2 are each a single species or multiple species of substituted or unsubstituted monovalent hydrocarbon group (refer to Japanese Patent Application Laid Open Number 62-41228 which is equivalent to U.S. Pat. No. 4,722.987).
A drawback to the first method is the partial gelation of the organopolysiloxane product when this method is applied to the preparation of SiH containing organopolysiloxane. While the second method does lead to depletion of the silanol in the organopolysiloxane product, it requires the use of expensive silazane or silylamine. Because the second method also requires the addition of water in an amount approximately equimolar with the silazane or silylamine, another problem with this particular method is the gelation of a portion of the organopolysiloxane product when this method is applied to the preparation of SiH-containing organopolysiloxane. Moreover, the aqueous ammonia generated by silazane (or silylamine) hydrolysis in the second method causes a partial cleavage of the organopolysiloxane main chain. The resulting silanol groups react with the introduced organosilicon compound to produce a molecular chain end group concentration which is higher than the theoretical molecular chain end group concentration. This causes the reproducibility of the degree of polymerization to be poor for the organopolysiloxane product.